1. Field
Aspects of embodiments of the present invention relate to an inkjet printhead and an apparatus and method for manufacturing an organic luminescence display using the inkjet printhead.
2. Description of the Related Art
Displays, which display various information on a screen, are core technology of the information and telecommunication age and are developing into thinner, lighter, portable, and high-performance displays. Accordingly, flat panel displays (such as organic luminescence displays) which can overcome disadvantages (i.e. weight and volume) of cathode ray tubes (CRTs) are attracting a lot of attention. An organic luminescence display is a self-emitting device that uses a thin organic light-emitting layer between electrodes. The organic luminescence display can be made as thin as paper. Organic luminescence displays can be classified into small-molecule organic luminescence displays and polymer organic luminescence displays according to the material of an organic light-emitting layer that generates light. Generally, an organic light-emitting layer of a small-molecule organic luminescence display is formed as a thin film by vacuum deposition, and an organic light-emitting layer of a polymer organic luminescence display is formed as a thin film using a solution coating method such as spin coating or inkjet printing.
When an organic light-emitting layer is formed by inkjet printing, organic light-emitting ink, which includes an organic light-emitting material and a solvent, is ejected from an inkjet printhead onto one or more pixels on a substrate in a display region, and then the ejected organic light-emitting ink is dried into the organic light-emitting layer. Here, when the organic light-emitting ink dries, it means that the solvent contained in the organic light-emitting ink evaporates. Typically, the solvent is highly volatile. Therefore, the solvent may be volatilized shortly after the organic light-emitting ink is ejected, thereby drying the organic light-emitting ink. Here, the concentration of molecules of the evaporating solvent (hereinafter, referred to as the concentration of evaporating solvent molecules) may be high in the center of a region to which the organic light-emitting ink was ejected and may be low at an edge of the region to which the organic light-emitting ink was ejected, that is, at a boundary between the region to which the organic light-emitting ink was ejected and a region to which the organic light-emitting ink was not ejected. This non-uniformity in the concentration gradient of the evaporating solvent molecules on the substrate may induce the evaporating solvent molecules to diffuse from the center of the region to which the organic light-emitting ink was ejected to the edge of the region to which the organic light-emitting ink was ejected. In addition, the edge of the region to which the organic light-emitting ink was ejected may dry relatively faster than the center of the region to which the organic light-emitting ink was ejected. Therefore, an organic light-emitting layer of a pixel located at the edge of the region to which the organic light-emitting ink was ejected may be concentrated toward the outside of the region. That is, the organic light-emitting layer of the pixel at the edge of the region to which the organic light-emitting ink was ejected may have a non-uniform thickness. The non-uniform thickness directly affects the display quality of the organic luminescence display.